Method and apparatus for the thermal analysis of metallic melts

ABSTRACT

Method and apparatus for the thermal analysis of metallic melts, in particular molten carbon steels, involving the use of permanently immersed, non-expandable thermocouples.

[ Nov. 27, 1973 expandable Johnston.......

ABSTRACT 3,250,125 5/1966 3,546,921 12/1970 Bourke et al.

Primary Examiner-Richard C. Queisser Assistant ExaminerJoseph W. RoskosAtt0meyTab T. Thein Method and apparatus for the thermal analysis ofmetallic melts, in particular molten carbon steels, involving the use ofpermanently immersed, non thermocouples.

THERMAL ANALYSIS OF METALLIC MELTS [75] Inventors: Hans-Rudiger Dorst,Berlin;

Helmut Zielinski, Muhlhausen, both of Germany [73] Assignee:VEBQualities-undEdelstahl- Kombiast Henningsdorf-kr., Oranineburg,Germany May 6, 1971 Appl. No.2 140,716

73/17 R, 73/343 R, 73/359 G01n 25/04, GOlk 7/02 73/61'R, 61LM,17 R,

References Cited UNITED STATES PATENTS 10/1971Shear-man.........................

United States Patent Dorst et al.

[ METHOD AND APPARATUS FOR THE [22] Filed:

[51] Int.

[58] Field of PATENTED "UV 2 7 I975 SAII 7 1 /1,

TIME

INVENTORS HANS-RUDIGER DORST HELMUT ZIELINSKI METHOD AND APPARATUS FORTHE THERMAL ANALYSIS OF METALLIC MELTS' It is known to utilize theeffect of the meltingtemperature drop of a metal, resulting from theaddition thereto of an alloying constituent, particularly carbon tosteel, in order to determine the percentage ratio. This is accomplishedby taking a sample from the metal melt and determining thesolidification temperature by means of a thermocouple (for example, anexpendable, so-called lost head lTec-tip-S method/). The alloyingpercentageratio is then obtained by comparing the theoreticaltemperature of the pure liquid metal with the measured solidifictiontemperature of the metal melt.

A shortcoming of this measuring method resides in that each testrequires the sacrifice of a protective tube or even an entire test head,including a thermocouple element, because the latter remains frozen inthe solidified melt, and each measurement involves taking a sample andfilling it into an ingot mOldfI'hisrequirement obviously reduces theaccuracy of the measurement and renders the method less dependable.

As a result of the high temperatures of the melt surrounding theimmersed thermocouple elements and the presence 'of readily reactive andpotentially corrosive gases and other harmful substances containedtherein, the elements are subjected to intensive embrittlement broughtabout by the heat, as well as to contamination of the wire elements orjunctions, which leads to errors and to rapid wear of the measuringelements.

Attempts have been made to extend the useful life of the thermocoupleelements by employing disposable one-time measuring points, so-calledlost headsf In a different approach to this problem, a wide selection ofdifferent material combinations has been tested both for the protectivetubes and for the measuring wires themselves, with various degrees ofsuccess.

When using thermocouples to take temperature measurements of the metalmelts it is also known to protect them by arranging for a stream ofargon or other inert gas to be blown past or about the measuring pointsso as to blow or rinse away corrosive gases which entered Y through theprotective tube or in some other way, or to keep them thus from thetips.

It is an important object of this invention to eliminate theshortcomings of the prior-art methods and substantially to extend theuseful life of thermocouple elements.

More specifically, it is the object of this invention to provide amethod and an apparatus for the thermal analysis of metallic melts, inparticular molten carbon steels, by means of permanently immersed,nonexpendable thermocouples, which permit to determine the temperatureof the liquid metal melt while at the same time substantially reducingthe danger of thermal embrittlement and contamination of thethermocouple elements.

In accordance with an important feature of the invention this objectiveis attained by employing a thermocouple element in a protective tube,permanently immersed in the melt which is either directly or indirectlycooled, with a layer originating from the surrounding metal melt beingfrozen onto the protective tube by the direct and/or indirect cooling,and following the cooling down of the thermocouple element to thesolidification temperature of the frozen-on layer, the cooling procedureis interrupted, and whereupon'the temperature of the melt is determinedwith the thermocouple,

the latter then being purged by direct and/or indirect cooling.

The method of the present invention is further characterized in that agaseous or liquid rinsing medium is used for direct cooling of thethermocouple element, which rinsing medium is non-reactive with respectto the combinations of materials adopted for the thermocouple elements.

An indirect cooling for the element, to act in an auxiliary oralternative capacity, can be provided by arranging a closed,disconnectible cooling unit inside the protective tube, in the area ofthe thermocouple measuring tip itself.

To be more specific, the following variants, adapted from the basicinventive method can be carried out:

1. Determining the temperature of a melt: measuring the temperature thenpurging again measuring the temperature.

H. Determining the alloying percentage of one of the chief constituentsof a melt: I

1. Freezing on a layer measuring the melting-on temperature purgingagain freezing on a layer.

2. Freezing on a layer (at purging or regeneration temperature)measuring the melting-on temperature again freezing on a layer.

III. Determining the temperature and the alloying percentage of one ofthe chief constituents of a melt:

1. Measuring the temperature freezing on a layer measuring themelting-on temperaure then purging again measuring the temperature.

2. Measuring the temperature freezing on a layer (at regenerationtemperature measuring the melting-on temperature again measuring thetemperature.

In the method variants listed hereinabove the sequence of the individualmethod steps, i.e. measuring the temperature, measuring the melting-ontemperature and purging can of course be varied according to needs.

To save time, purging of the thermocouple element can preferably takeplace between the temperaturemeasuring and the subsequent indirectalloyingpercentage determination steps since the thermocouple elementmust be made to cool when determining the solidification temperature.

When freezing or solidifying a layer of the melt material ontotheprotective tube, the thermocouple element can be cooled to theregeneration temperature so that additional purging of the element canbe dispensed with.

Periodical purging protects the thermocouple to a large degree fromcontamination and from thermally caused embrittlement, and thus greatlyextends its useful life.

The periodically undertaken temperature measurements and the likewisealternate periodical determination of the alloying percentage of one ofthe chief constituents make it possible rapidly to obtain measuredvalues of the principal parameters which influence the metal melt (suchas temperature and alloying ratio), and thus assure a satisfactorydegree of control over the process as it develops, so as to prepare analloy of predetermined quality and composition. Hence, the removal ofmelt samples for testing can be greatly reduced; as it is, the resultsof such tests are available only with a certain delay, i.e., at a timewhen the momentary state of the melt may have already undergoneconsiderable changes.

Other objects and many of the attendant advantages of the invention willbe readily appreciated as the same becomes better understood byreference to the following detailed description, when considered withthe accompanying drawing, wherein FIG. 1 shows in cross-section animmersion-type thermocouple element adapted for permanent immersion andbeing rinsed, accommodated in a wall of a schematically shownmetal-smelting furnace, and

FIGS. 2 and 3 are diagrams showing the respective temperature andcooling-intensity patterns as recorded by the thermocouple according tothe invention during the individual phases of the new method.

Referring now to FIG. 1, numeral 1 identifies a wall of a metal-smeltingfurnace, in which is accommodated a thermocouple element 2, insertedinto a protective tube 3 made, for example, of aluminum oxide orzirconium oxide. The ambient temperature of element 2 is measured on thebasis of the prevailing voltage, which is a function of the melttemperature, by means of a voltmeter 7. To provide direct cooling andpurging for thermocouple element 2, the head of the measuring probe,which is arranged outside furnace wall 1, is equipped with an inlet 4and an outlet 5 for a cooling medium, through which can be made tocirculate a cooling and/or rinsing medium stream which thus passes overthermocouple element 2.

It will be noted from FIG. 1 of the drawing that the protective tube 3,with the thermocouple therein, is removably inserted in a wall of thefurnace, e.g. by means of screws and the like, identified by numeral 8.

Since purging and measuring of the melting temperature require differentcooling outputs, a regulating valve (not shown) is conneced by suitabletubes to both element 2 and a coolant container (not shown) so that thecoolant stream can be regulated within narrow tolerances as a functionof coolant pressure, tube crosssection and the specific method variantselected.

Non-reactive gases or liquids, such as for example argon, nitrogen,carbon dioxide and the like can be employed for the direct cooling ofthermocouple 2; they are passed through inlet 4 for element 2 in orderto protect the latter from contamination and thermal embrittlement, andalso to cool protective tube 3 in order to freeze a layer of the meltmaterial thereon.

A closed, disconnectible cooling unit 6 is arranged inside tube 3,within the area of thermocouple element 2 itself; it can be used inaddition to the main or direct cooling and/or rinsing system whichoperates with a coolant stream, or alternatively thereto.

Cooling unit 6 can be provided in the form of, e.g., a cooling jacket orcoil; it is connected with the earliermentioned coolant container orwith a pump (not shown) by means of appropriate tubing 6a.

To purge the thermocouple element, i.e., eliminate the possibility of acorrosion of the thermocouple junction by reactive gases which may havepenetrated into brittlement of the junctions or contacts, element 2 iscooled to a temperature substantially below its normaltemperature-measuring range, and intensively rinsed by passing thereovera chemically non-reactive rinsing medium. To save time, the coolingeffect can be intensified by switching on the closed cooling system 6.It is, of course, also possible to use unit 6 alone for purging itsprotecn've tubing, and in order to avoid thermal emthermocouple element2, particularly when the junctions show only a moderate tendency tobecome corroded and penetrated gases.

The determination of the alloying percentage of one of the chiefconstituents of the melt, which is made indirectly by the intermediaryof the melting temperature, likewise requires a direct and/or indirectcooling in order to cause the freezing of a lyaer of the melt materialonto protective tube 3. After such a layer is applied to tube 3, thecoolant stream for direct and/or indirect cooling, the latter by meansof cooling unit 6, is turned off and the melting-on temperature of thefrozen" layer is measured. The alloying percentage is then determined bycomparing the measured meltingon temperaure with the theoretical liquidtemperature of the other chief constituent of the alloy.

The diagrams of FIGS. 2 and 3 display successive time intervals A, B, Cand D (not necessarily identical) in which the phases or steps of theinventive method are carried out. In both diagrams, the solid lineindicates the course of a periodical temperature determination ormeasurement while the interrupted line corresponds to the course of atemperature measurement combined with a determination of the alloyingpercentage, as has been explained earlier in the groups I., II., III.and subgroups thereof. In phase or time period D, the latter may havetwo variants, bifurcated and identified by letters a and b.

To summarize, the two diagrams illustrate the course of the temperature(C) and cooling intensity (Q), respectively, in the function of time,namely I. for a periodical temperature measurement (solid lines) in whihthe following steps are performed;

A measuring the temperature B purging C again measuring the temperature;and

II. for a combined temperature alloying-percentage determination(unbroken lines) with the following steps A measuring thetemperature Bfreezing on a layer at regeneration temperature C measuring themelting-on temperature D variant a: purging, or

b: measuring the temperature, substantially as was explained in theearlier-presented groups I and HI, respectively, which illustrate theprocedural variants of the inventive method which can be practised.

It should be understood, of course, that the foregoing disclosurerelates only to preferred embodiments of the invention and that is isintended to cover all changes and modifications of the exemplaryprocedures and arrangements described which do not constitute departuresfrom the spirit and scope of the invention.

Reference should be had, in closing, to a concurrently filed patentapplication entitled Differential Thermoelements, by one of the presentinventors, Hans-Ruediger Dorst, Ser. No. 140,750, with disclosuredetails which supplement the preset application.

What we claim is: l. A method for the thermal analysis of melts, such.as of molten carbon steels, with the aid of a nonexpendablethermocouple inserted in a removal protective tube and immersed in theliquid melt, comprising thesteps of freezing on a layer from thesurrounding melt onto the protective tube by introducing a coolant intothe tube and thus cooling the thermocouple therein, determining thesolidification temperature of the frozen-on layer by the aid of thethermocouple, purging the latter by further introduction of the coolantwith resulting further cooling thereof, substantially below itstemperature measuring range, interrupting the coolant flow to the tube,and determining the temperature of the melt by means of thethermocouple.

2. The method as defined in claim 1 wherein said step of freezing on alayer onto the protective tube includes said purging step by furthercooling the thermocuple to its purging temperature.

3. The method as defined in claim 1, wherein said step of cooling thethermocouple is carried out by the aid of a gaseous or liquid rinsingmedium which is nonreactive with respect to the materials of thethermocouple and the protective tube.

4. An apparatus for the thermal analysis of melts,

such as molten carbon steels, comprising: a nonexpendable thermocouple,including a removable protective tube immersed in the liquid melt; meansfor introducing a coolant into said tube, circulating the same aboutsaid thermocouple and discharging the same from said tube, thereby tocool said thermocouple; and a closed, disconnectible cooling unitsurrounding said thermocouple the form of a cooling jacket, and beingdisposed within said protective tube.

5. The apparatus as defined in claim 4, wherein said means forintroducing, circulating and discharging the coolant includes means forcirculating a gaseous or liquid rinsing medium in said protective tube,which is non-reactive with respect to the materials of said thermocoupleand said tube.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO.5,774,441 DATED November 2'7, 1975 INVENIOR(S) Hans-Rudiger Dorst et alIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Correct the Assignee ['75] to read: VEB Qualitlts: undEdelstahl-Kombinat, Hennigsdorf/Kr. Oranienburg, Germany;

Column 1, line 10, correct the spelling of "Tectip-S";

line 15, correct the spelling of "solidifcation";

column 2, line 14, change "variants," to variants line 55, change"temperature" to temperature) column 4, line 5, change and" to by line8, correct the spelling of "layer"; line 55, correct the spelling of"which"; lines 45 and 44, change to read:

- D variant a: purging, or

I b: measuring the temperature,

line 65 (claim 1, line 5) change "removal" to removable column 5, line 8(claim 2, line 1) change "1" to l,

line 10 5) correct the spelling of "thermocouple"; and

column 6, line 8 (claim 4, line 9) before "the form" insert in finallycolumn 4, line 59, change "preset application." to present application,now U.S. Patent 5,757,206 dated September 4,

Signed and Scaled this twenty-second Day Of June 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ufParemsand Trademarks

1. A method for the thermal analysis of melts, such as of molten carbonsteels, with the aid of a non-expendable thermocouple inserted in aremoval protective tube and immersed in the liquid melt, comprising thesteps of freezing on a layer from the surrounding melt onto theprotective tube by introducing a coolant into the tube and thus coolingthe thermocouple therein, determining the solidification temperature ofthe frozen-on layer by the aid of the thermocouple, purging the latterby further introduction of the coolant with resulting further coolingthereof, substantially below its temperature measuring range,interrupting the coolant flow to the tube, and determining thetemperature of the melt by means of the thermocouple.
 2. The method asdefined in claim 1 wherein said step of freezing on a layer onto theprotective tube includes said purging step by further cooling thethermocuple to its purging temperature.
 3. The method as defined inclaim 1, wherein said step of cooling the thermocouple is carried out bythe aid of a gaseous or liquid rinsing medium which is non-reactive withrespect to the materials of the thermocouple and the protective tube. 4.An apparatus for the thermal analysis of melts, such as molten carbonsteels, comprising: a non-expendable thermocouple, including a removableprotective tube immersed in the liquid melt; means for introducing acoolant into said tube, circulating the same about said thermocouple anddischarging the same from said tube, thereby to cool said thermocouple;and a closed, disconnectible cooling unit surrounding said thermocouplethe form of a cooling jacket, and being disposed within said protectivetube.
 5. The apparatus as defined in claim 4, wherein said means forintroducing, circulating and discharging the coolant includes means forcirculating a gaseous or liquid rinsing medium in said protective tube,which is non-reactive with respect to the materials of said thermocoupleand saId tube.